[BUG] URL cannot pass to Drop And Fetch components

[Lin064]

Describe the bug
In "Build Visualization From problem page"(page 1), the URL cannot pass to backend.

To Reproduce
Steps to reproduce the behavior:

1. Problem Animation Build Page.
2. Type any URL into URL text filed.
3. Print the URL detail in backend API(host:8000/upload/pddl).
4. See the URL always empty

Expected behavior
Backend can receive the URL.